Engines may be configured with various fuel systems used to deliver a desired amount of fuel to an engine for combustion. One type of fuel system includes a port fuel injector and a direct fuel injector for each engine cylinder. The port fuel injectors may be operated to improve fuel vaporization and reduce engine emissions, as well as to reduce pumping losses & fuel consumption at low loads. The direct fuel injectors may be operated during higher load conditions to improve engine performance and fuel consumption at higher loads. Additionally, both port fuel injectors and direct injectors may be operated together under some conditions to leverage advantages of both types of fuel delivery.
Engines operating with both port fuel injectors and direct injectors may operate for extended periods without using the direct injectors. During periods of non-use, the direct injector tips are exposed to high temperatures within the combustion cylinders resulting from the combustion of fuel injected from the port fuel injectors. Further, the increased temperature at the direct injector may lead to the vaporization of fuel within the direct injector. This may lead to fuel distillation within the injector tip, which may lead to deposits internal to the injector, and in turn affect the durability of the direct fuel injector.
The direct injectors may be cooled by periodically injecting fuel from the direct fuel injectors during operation of the vehicle. However, the inventors herein have recognized problems with this approach. As one example, it may be desirable to run maximum sustained PFI operation for improved fuel economy and reduced emissions. In another example, the direct fuel injectors may be coupled to a limited supply of fuel, which may thus be depleted and not be available when needed if fuel is constantly injected. Further, the periodic injection of fuel through the direct injectors may not be sufficient to prevent vapor space formation within the portions of the injector exposed to the heat of combustion within the engine cylinders.
In one example, some of the above described issues may be addressed with a method, comprising: during engine cylinder operation with fuel from a first injector and not a second injector: increasing a rail pressure of a fuel rail coupled to the second injector in response to a temperature increase of a tip of the second injector. In this way, an engine cylinder may be operated by combusting fuel from the first injector without affecting durability of the second injector. By raising the rail pressure of a fuel rail coupled to the second injector in response to a temperature increase of a tip of the second injector, the method may be utilized to prevent a vapor space from forming within the second injector, for example, within the tip of the second injector which is exposed to the heat of combustion within the engine cylinder. By preventing a vapor space from forming, the method may be used to prevent fuel distillation in the tip of the second injector during periods where the engine cylinder is operating with fuel from a first injector and not the second injector.
In another example, some of the above issues may be addressed by a fuel system for an internal combustion engine, comprising: a group of direct fuel injectors in communication with a group of cylinders, respectively; a first fuel rail in communication with the group of direct fuel injectors; a high-pressure fuel pump in communication with the first fuel rail; and a control system configured with instructions stored in memory for: during a first condition, increasing a rail pressure in the first fuel rail by operating the high-pressure fuel pump when a temperature of a tip of one or more of the group of direct injectors exceeds a first threshold. In this way, the fuel system may be utilized to regulate the pressure in the first fuel rail in response to an increased temperature by operating the high pressure fuel pump. The rail pressure of the first fuel rail may be regulated as a function of injector tip temperature. Thus, the high pressure fuel pump may be used to raise the fuel rail pressure to a pressure such that liquid fuel in the first fuel rail remains in liquid form.
In yet another example, some of the above issues may be addressed by a method, comprising: operating an engine cylinder with fuel from a first injector and not a second injector; during a first condition, increasing a rail pressure of a fuel rail coupled to the second injector in response to a temperature increase of a tip of the second injector; and during a second condition, injecting fuel from the second injector into the engine cylinder in response to the temperature increase. In this way, liquid fuel may be injected by the second injector, thus cooling the injector in response to the temperature increase. Further, liquid fuel injection may be limited to specific operating conditions, thus maintaining or improving engine emissions and fuel economy during operation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.